Datasheet

Data Sheet AD5689/AD5687
Rev. 0 | Page 23 of 24
APPLICATIONS INFORMATION
MICROPROCESSOR INTERFACING
Microprocessor interfacing to the AD5689/AD5687 is achieved
via a serial bus using a standard protocol that is compatible with
DSP processors and microcontrollers. The communications
channel requires a 3-wire or 4-wire interface consisting of a clock
signal, a data signal, and a synchronization signal. Each device
requires a 24-bit data-word with data valid on the rising edge
of
SYNC
.
AD5689/AD5687 TO ADSP-BF531 INTERFACE
The SPI interface of the AD5689/AD5687 is designed to be
easily connected to industry-standard DSPs and microcontrollers.
Figure 43 shows the AD5689/AD5687 connected to an Analog
Devices Blackfin® DSP. The Blackfin has an integrated SPI port
that connects directly to the SPI pins of the AD5689/AD5687.
Figure 43. ADSP-BF531 Interface to the AD5689/AD5687
AD5689/AD5687 TO SPORT INTERFACE
The Analog Devices ADSP-BF527 has one SPORT serial port.
Figure 44 shows how one SPORT interface can be used to
control the AD5689/AD5687.
Figure 44. SPORT Interface to the AD5689/AD5687
LAYOUT GUIDELINES
In any circuit where accuracy is important, careful consideration of
the power supply and ground return layout helps to ensure the
rated performance. Design the PCB on which the AD5689/
AD5687 are mounted so that the AD5689/AD5687 lie on the
analog plane.
Provide the AD5689/AD5687 with ample supply bypassing of
10 µF in parallel with 0.1 µF on each supply, located as close to
the package as possible, ideally right up against the device. The
10 µF capacitor is of the tantalum bead type. Use a 0.1 µF capa-
citor with low effective series resistance (ESR) and low effective
series inductance (ESI), such as the common ceramic types,
which provide a low impedance path to ground at high frequencies
to handle transient currents due to internal logic switching.
In systems where there are many devices on one board, it is
often useful to provide some heat sinking capability to allow
the power to dissipate easily.
Each AD5689 or AD5687 has an exposed paddle beneath the
device. Connect this paddle to the GND supply for the part. For
optimum performance, use special considerations to design the
motherboard and to mount the package. For enhanced thermal,
electrical, and board level performance, solder the exposed
paddle on the bottom of the package to the corresponding
thermal land paddle on the PCB. Design thermal vias into the
PCB land paddle area to further improve heat dissipation.
The GND plane on the device can be increased (as shown in
Figure 45) to provide a natural heat sinking effect.
Figure 45. Paddle Connection to Board
GALVANICALLY ISOLATED INTERFACE
In many process control applications, it is necessary to provide
an isolation barrier between the controller and the unit being
controlled to protect and isolate the controlling circuitry from
any hazardous common-mode voltages that may occur. The
iCoupler® products from Analog Devices provide voltage
isolation in excess of 2.5 kV. The serial loading structure of the
AD5689/AD5687 makes these parts ideal for isolated interfaces
because the number of interface lines is kept to a minimum.
Figure 46 shows a 4-channel isolated interface to the AD5689/
AD5687 using an ADuM1400. For more information, visit
www.analog.com/icouplers.
Figure 46. Isolated Interface
ADSP-BF531
SYNC
SPISELx
SCLKSCK
SDINMOSI
LDACPF9
RESET
PF8
AD5689/
AD5687
11255-043
ADSP-BF527
SYNCSPORT_TFS
SCLKSPORT_TSCK
SDIN
SPORT_DTO
LDACGPIO0
RESETGPIO1
AD5689/
AD5687
11255-044
AD5689/
AD5687
GND
PLANE
BOARD
11255-045
ENCODE
SERIAL
CLOCK IN
CONTROLLER
ADuM1400
1
SERIAL
DATA OUT
SYNC OUT
LOAD DAC
OUT
DECODE
TO
SCLK
TO
SDIN
TO
SYNC
TO
LDAC
V
IA
V
OA
ENCODE DECODE
V
IB
V
OB
ENCODE DECODE
V
IC
V
OC
ENCODE DECODE
V
ID
V
OD
1
ADDITIONAL PINS OMITTED FOR CLARITY.
11255-046